Friction materials for these brake devices are produced by admixing a fibrous base substance, filler, etc. with a thermosetting resin (such as a phenolic resin or epoxy resin) as a binder and pressing the mixture into a body with heating and application of pressure.
Friction materials capable of retaining a high coefficient of friction over a wide temperature range with good stability are required for use in brake devices for motor vehicles so as to render the device compact and lightweight.
Friction materials conventionally in use have incorporated therein chrysotile asbestos serving as the fibrous base substance, whereas with an increase in the temperature of the friction surface these friction materials become markedly worn or damaged and are susceptible to a fading phenomenon involving a marked reduction in the coefficient of friction. Chrysotile asbestos further has the problem of being carcinogenic.
Friction materials of the non-asbestos type are known which comprise fibers of potassium hexatitanate (K.sub.2 Ti .sub.6 O.sub.13) of tunnel-type crystal structure in place of chrysotile asbestos fibers. These materials have better friction-wear characteristics than chrysotile asbestos fibers but the anti-fading properties and coefficient of friction of these materials are not enough at the high temperature.
Friction materials are also proposed wherein calcium titanate (CaTiO.sub.3) in the form of a powder or fibers is used instead of fibers of alkali metal titanate like potassium hexatitanate (Japanese pre-examination publication HEI 8-53553). Calcium titanate is a synthetic inorganic compound having a crystal structure of the perovskite type. The presence of this compound affords friction-wear characteristics superior to those of the friction material which adds a powder of alkali metal hexatitanate compound. However, preparation of calcium titanate by solid-phase synthesis requires a heat treatment at a temperature of over 1300.degree. C., consequently producing coarse crystals which come to cause sintering easily. The friction materials which add the powder of large crystal particles cause an inconvenience wherein the adjoining materials are severely abraded. Further when sintering is caused, after heat-treatment the crushing stage and the classifying stage are needed, while the crushed crystal particles are angular and more likely to abrade the adjoining materials.
An object of the present invention is to provide a powder of titanium compounds which, when this material is used as the base substance of friction materials, gives a higher coefficient of friction to the materials and can reduce the abrasion to the adjoining materials.